Originally posted by pro_keyboardconsultant:
Their sandcast plate instead of a vacuum sealed plate helps elimate harsh overtones often found in less expensive baby grands.
From my experience with different types of metal casting processes, either method should produce an acceptable iron casting. The purpose of the plate is to provide a very low-Q supporting structure for the the strings and the alloys used in either case are probably identical. Cast iron is very good in this regard. It can also deal very well with compression loads. It's similar to concrete. Someone should build a concrete plate!
I would guess that those few aluminum plates from the last century probably didn't work very well since the plate should be acoustically dead.
The major differences appear when looking at the economics of which method to use. So called "sand-casting" can use purely gravity to fill the mold, which for a large piece can be difficult to control. That's why many old pianos develop cracks because of old flaws in the structure. This type of casting is usually good for smaller volumes.
I'm not sure what's meant by a "vacuum sealed" plate. Probably doesn't mean it's wrapped in plastic.
More likely it is "vacuum assisted" where gravity is helped by a vacuum pump to help fill the mold and eliminate voids, whether it is sand,resin, rubber or whatever type of mold. If you're making a lot of plates, one would want to maximize the yield and this is one way of doing it. Also, this is a good way of promoting consistency between plates when used in concert with a accurate casting method like a tooled steel mold. A consistently produced plate can improve yield further down the manufacturing process, like when it comes time to fit it to the cabinet.
There appears to be some folklore surrounding "sand casting" since "that's the way they did it back in the 19th century" and its recent use as a selling point.